This application claims the priority of Swiss Application No. 2000 0162/00 filed Jan. 27, 2000, which is incorporated herein by reference.
In packing machines which package items into wrapper sleeves, first a film sleeve is formed about the items and then the sleeve is longitudinally sealed. In a transverse sealing station transverse seams are formed between the items and subsequently the transverse seams are severed in their center across the sleeve to thus obtain individual packages.
In European Patent No. 399 948 to which corresponds U.S. Pat. No. 5,052,166, a transverse sealing station is described which has facing sealing shoes and counter shoes provided with cylindrical sealing faces and counter faces. The sealing faces are arranged coaxially with and revolve about respective rotary axes. The maximum advancing speed of the sleeve is limited where such transverse sealing stations are used because of the delay in heat transfer from the sealing shoes through the film to the sealing layer.
To take into consideration such a delay, it is further known to provide sealing shoes and counter shoes which, while they rotate, they also co-travel with the wrapper sleeve. Such an arrangement which increases the output of the packing machine, is described, for example, in published International Application WO 96/17720 to which corresponds U.S. Pat. No. 5,771,660. The transverse sealing station described therein is, however, of relatively complex structure and is therefore expensive to manufacture and service. Further, the masses moved back and forth parallel to the conveying direction of the wrapper sleeve cause oscillations which are transmitted to the entire packing machine.
It is an object of the invention to provide an improved apparatus of the above-outlined type with which a high packing capacity may be achieved with simple structural means.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the apparatus for sealing a wrapper sleeve includes a first sealing shoe having a first peripheral surface supported for rotation about a first axis. The first peripheral surface has a generatrix being parallel to and at a maximum distance from, the first axis and a radius of curvature which is smaller at any point of the circumferential length of the first peripheral surface than the maximum distance. A second sealing shoe, having a second peripheral surface is supported for rotation about a second axis oriented parallel to the first axis. The first and second peripheral surfaces together define a line of contact with one another with the wrapper sleeve interposed therebetween. The first and second sealing shoes rotate in synchronism whereby the first and second peripheral surfaces roll on one another effecting sealing of the wrapper sleeve as the wrapper sleeve is advanced. A device displaces the first axis relative to the second axis in a direction transverse to the advancing direction of the wrapper sleeve for effecting displacement of the line of contact in the advancing direction as the first and second sealing shoes rotate.